1. Field of the Disclosure
Embodiments disclosed herein relate generally to crosslinked foams suitable for use as a shock absorbing layer. In another aspect, embodiments disclosed herein relate to crosslinked foams useful in footwear, such as part of a shoe or boot, including soles, midsoles, or a complete shoes or boot. In another aspect, embodiments described herein relate to a synthetic turf and other flooring applications including a crosslinked foam shock absorbing layer, where the foam may include up to 50% of a filler.
2. Background
Conventional articles of footwear include two primary elements, an upper and a sole structure. The upper provides a covering for the foot that securely receives and positions the foot with respect to the sole structure. In addition, the upper may have a configuration that protects the foot and provides ventilation, thereby cooling the foot and removing perspiration. The sole structure is secured to a lower surface of the upper and is generally positioned between the foot and the ground. In addition to attenuating ground reaction forces, the sole structure may provide traction and control potentially harmful foot motion, such as over-pronation. Accordingly, the upper and the sole structure operate cooperatively to provide a comfortable structure that is suited for a wide variety of ambulatory activities, such as walking and running. The general features and configuration of the upper and the sole structure are discussed in greater detail below.
The upper forms a void on the interior of the footwear for receiving the foot. The void has the general shape of the foot, and access to the void is provided by an ankle opening. Accordingly, the upper extends over the instep and toe areas of the foot, along the medial and lateral sides of the foot, and around the heel area of the foot. A lacing system is often incorporated into the upper to selectively increase the size of the ankle opening and permit the wearer to modify certain dimensions of the upper, particularly girth, to accommodate feet with varying proportions. In addition, the upper may include a tongue that extends under the lacing system to enhance the comfort of the footwear, and the upper may include a heel counter to limit movement of the heel.
Various materials may be utilized in manufacturing the upper. The upper of an article of footwear, for example, may be formed from multiple material layers that include an exterior layer, a middle layer, and an interior layer. The materials forming the exterior layer of the upper may be selected based upon the properties of wear-resistance, flexibility, and air-permeability, for example. With regard to the exterior layer, the toe area and the heel area may be formed of leather, synthetic leather, or a rubber material to impart a relatively high degree of wear-resistance. Leather, synthetic leather, and rubber materials may not exhibit the desired degree of flexibility and air-permeability. Accordingly, various other areas of the exterior layer of the upper may be formed from a synthetic textile. The exterior layer of the upper may be formed, therefore, from numerous material elements that each imparts different properties to specific areas of the upper.
A middle layer of the upper may be formed from a lightweight polymer foam material that attenuates ground reaction forces and protects the foot from objects that may contact the upper. Similarly, an interior layer of the upper may be formed of a moisture-wicking textile that removes perspiration from the area immediately surrounding the foot. In some articles of athletic footwear, the various layers may be joined with an adhesive, and stitching may be utilized to join elements within a single layer or to reinforce specific areas of the upper.
The sole structure generally incorporates multiple layers that are conventionally referred to as an insole, a midsole, and an outsole. The insole is a thin, comfort-enhancing member located within the upper and adjacent the plantar (lower) surface of the foot to enhance footwear comfort. The midsole, which is traditionally attached to the upper along the entire length of the upper, forms the middle layer of the sole structure and serves a variety of purposes that include controlling foot motions and attenuating ground reaction forces. The outsole forms the ground-contacting element of footwear and is usually fashioned from a durable, wear-resistant material that includes texturing to improve traction.
The primary element of a conventional midsole is a resilient, polymer foam material, such as polyurethane or ethylvinylacetate, which extends throughout the length of the footwear. The properties of the polymer foam material in the midsole are primarily dependent upon factors that include the dimensional configuration of the midsole and the specific characteristics of the material selected for the polymer foam, including the density of the polymer foam material. By varying these factors throughout the midsole, the relative stiffness, degree of ground reaction force attenuation, and energy absorption properties may be altered to meet the specific demands of the activity for which the footwear is intended to be used.
Various foams also find use as a shock-absorbing layer in artificial turf. Artificial turf consists of a multitude of artificial grass tufts extending upward from a sheet substrate. The turf is usually laid upon a prepared, flat ground surface to form a game playing field intended to simulate a natural grass playing field surface.
For some types of games, a resilient underpad is placed beneath the turf and upon the firm ground support surface to provide a shock absorbing effect. Also, in some instances, a layer of sand or other particulate material is placed upon the upper surface of the carpet base sheet and around the strands. An example of this type of construction is shown in U.S. Pat. No. 4,389,435 issued Jun. 21, 1983 to Frederick T. Haas, Jr. Another example is shown in U.S. Pat. No. 4,637,942 issued Jan. 20, 1987 to Seymour A. Tomarin.
Further, examples of artificial turfs which are formed with the grass-like carpet placed upon a resilient underpad are disclosed in U.S. Pat. No. 3,551,263 issued Dec. 29, 1970 to Carter et al., which discloses a polyurethane foam underpad; U.S. Pat. No. 3,332,828 issued Jul. 25, 1967 to Faria et al., which discloses a PVC foam plastic or polyurethane foam plastic underpad; U.S. Pat. No. 4,637,942 issued Jan. 20, 1987 to Seymour A. Tomarin which discloses a rubber-like underpad; U.S. Pat. No. 4,882,208 issued Nov. 21, 1989 to Hans-Urich Brietschidel, which illustrates a closed cell crosslinked polyethylene foam underpad; U.S. Pat. No. 3,597,297 issued Aug. 3, 1971 to Theodore Buchholz et al., which discloses a polyurethane underpad having voids; and U.S. Pat. No. 4,505,960 issued Mar. 19, 1985 to James W. Leffingwell, which discloses shock absorbing pads made from elastomer foams of polyvinyl chloride, polyethylene, polyurethane, polypropylene, etc.
Shock absorbing layers may, of course, be more broadly used in other applications, such as in energy dampening in floors and shockpads for shoes, for example. What is still needed, therefore, are improved materials and methods for forming shock absorbing layers. There also exists a need for improved materials that may be used to form portions of a shoe or boot, including the sole, midsole, or other various portions of a shoe.